RICHMOND — Virginia Attorney General Mark R. Herring filed a civil suit Friday against the builders of the Mountain Valley Pipeline, a major natural-gas project in the southwestern part of the state, alleging they violated state environmental laws by failing to control sediment and storm-water runoff.

The project stretches 300 miles from West Virginia through some of Virginia’s most rugged mountains and into North Carolina. It is being built by a consortium of companies led by EQT Midstream Partners of Pittsburgh.

Herring (D), joined by the Virginia Department of Environmental Quality, charges that the builders violated regulations requiring the protection of streams and steep mountain terrain.

“This suit alleges serious and numerous violations of environmental laws that caused unpermitted impacts to waterways and roads in multiple counties in Southwest Virginia,” Herring said in a news release. “We’re asking the court for an enforceable order that will help us ensure compliance going forward, and for penalties for MVP’s violations.”

A spokeswoman for the builders blamed the problems on unexpectedly severe weather.

“The unusually wet conditions and periods of record rainfall this year in Virginia have presented construction challenges, and the MVP project team has worked diligently to ensure appropriate soil erosion and sediment controls were implemented and restored where necessary along the route,” spokeswoman Natalie Cox said.

The MVP is the shorter of two major gas pipelines being built across Virginia. The other, the 600-mile Atlantic Coast Pipeline, is being built by a consortium led by Dominion Energy and crosses through central Virginia.

That project also faced a setback Friday, as three judges of the U.S. Court of Appeals for the 4th Circuit issued a stay against a permit from the Fish and Wildlife Service regulating that pipeline’s impact on endangered species. The court had earlier found that the permit was hastily issued, and it granted the stay at the request of environmental groups so the new permits can be more closely reviewed.

Herring’s suit against the MVP comes as environmental groups have slammed the administration of Gov. Ralph Northam (D) for seeming to clear the way for the pipeline projects. David Paylor, director of the state Department of Environmental Quality, said in a statement that the governor had empowered the department “to pursue the full course of action necessary to enforce Virginia’s environmental standards.”

Paylor said the department decided that referring the matter to Herring’s office was the fastest way to get the issues addressed.

“Today’s lawsuit holding the developers of the Mountain Valley Pipeline accountable for environmental devastation in Southwest Virginia is the show of leadership we’ve been waiting for from this Administration,” Michael Town, executive director of the Virginia League of Conservation Voters, said in an email.

The suit says the MVP builders committed “repeated environmental violations” in Craig, Franklin, Giles, Montgomery and Roanoke counties. It seeks “the maximum allowable penalties” and a court order to back up future enforcement.

According to Herring, inspectors from the DEQ found numerous violations during on-site visits from May through October. Separately, a contractor hired by the state also spotted more than 300 violations between June and November, Herring said. The violations allegedly resulted in heavy erosion and sediment clogging waterways.

Cox, the pipeline spokeswoman, noted that the builders had consulted with the DEQ in June and agreed at that time to suspend construction work to focus on erosion control.

“The MVP project team takes its environmental stewardship responsibilities very seriously and appreciates the guidance and oversight by the [DEQ],” Cox said in an email. “MVP will continue to comply with the relevant laws and regulations related to the safe and responsible construction of this important infrastructure project.”